Semidiurnal Fluctuations Research Articles

AN APPROACH TO QUANTIFY THE FLUCTUATION CHARACTERISTICS OF GROUNDWATER TABLE

Groundwater table fluctuations reflect the physical properties of the aquifer of a region. Especially, in a coastal region, sinusoidal fluctuations of groundwater levels occur in response to tide. If the level of bodies of surface water varies with a simple harmonic motion, a chain of sinusoidal waves may be propagated inland from the shore. Consequently, the water yield of a flowing well under the influence of tidal activity fluctuates correspondingly. So the author attempted to quantify the fluctuation char-acteristics of groundwater table levels in the flowing wells located at various distances from the river shore of the Tone. Data concerning the variation of groundwater levels were collected from three flow-ing wells in one line towards inland from the shore. The author's procedures are given below. (1) The fluctuation characteristics of daily and monthly yields of each well are expressed by the following equations respectively. _??_ where, Di denotes an absolute value of deviation from the mean monthly yield. Q is the discharge of a flowing well (l/min) M is the mean value of Q Qr, is the mean deviation of water yield (2) The statistics of frequency distribution of daily yield throughout a year is represented by Pd which is defined as the modal value of the Q. A cumulative curve like that of a flow duration curve is drawn, and from the graph the standard deviation of Q is calculated as the mean of the first and the third quartile deviation of water yield. The other measures proposed are as follows, QH : the yield which equalled or exceeded 95 days of the year. QM: the yield which equalled or exceeded 185 days of the year. QL : the yield which equalled or exceeded 355 days of the year. (3) The equation governing the groundwater behaviour in porous, isotropic media may be written in the form: _??_ where, Δh is the amplitude of groundwater fluctuations during a half tide cycle, and this value can be obtained from the flow duration curve and it generally tends to decrease with the distance from the shore. ΔH is the tidal range. x is the distance inland from the shore. σ is the angular velocity 28.98/hr during a semidiurnal fluctuation. k is a parameter which is equivalent to the coefficient of permeability and governed by the porosity of the aquifer. t is time. The above analysis suggests that the elastic property of confined aquifers results in changes in hydrostatic pressure when changes in loading occur. That is, an additional load compresses the aquifer and increases the hydrostatic pressure which is transformed into the potential head of a flowing well. After then, the pressure decreases and ap-proaches its original value as groundwater moves away. Field measurements of groundwater table variations in coastal region show that the parameter k proposed by the author in this work is a satisfactory representation of the groundwater dynamics for the studied area.

Seasonal variations in the effect of temperature on the respiration of certain intertidal algae

The intertidal algae Enteromorpha, Ulva, Fucus, Porphyra, Chondrus and Griffithsia are subjected to wide semi-diurnal fluctuations in temperature during the summer months. Measurements of the rate of respiration of such algae in the dark at a wide variety of temperatures have shown that during the summer the curve relating respiration to temperature (R. T curve) has a relatively shallow slope of Q10 < 1·2 between 10° and 20 °C. Algae collected during the autumn and winter show R. T curves which have a shallow slope in regions approximating to the temperature of the shore at the time of collection. Thus the respiration of such intertidal algae is relatively unaffected by temperature fluctuation within the normal environmental range. Further, the form of the R. T curve is not a fixed phenomenon which is characteristic of a particular species of alga, but appears to be modifiable in such a way that the shallow region of the R. T curve is appropriate to the temperatures prevailing in the habitat. In this way the effects of temperature fluctuation upon respiration are minimized.

Near-bottom currents measured in 4 kilometers depth off the Baja California Coast

Measurement of water currents 3 meters above the bottom in 3700 to 4300 meters depth from 300 to 800 km west of the northern Baja California coast shows a net transport of about 2.2 cm sec−1 toward the southeast and semidiurnal fluctuations of an rms amplitude of about 1.7 cm sec−1, rotating counterclockwise. Both motions are generally coherent over dimensions of the order of 200 or more km, and the phase of the fluctuations is also coherent with the tides at La Jolla, California, 400 to 800 km away. The fluctuating motion may be ascribed principally to surface tides, since random motions and incoherent internal tides contribute not more than one-half of the observed velocities. The observed tidal fluctuations involve a calculated unit-area power dissipation several orders of magnitude less than the oceanic mean.

Atmospheric tidal oscillations: an analysis of the mechanics

An approximate formula for the equivalent depth of a compressible atmosphere is developed and shows that Coriolis forces dominate the diurnal tide causing it to have a small scale depth. It follows that either the diurnal motion field is confined to the vicinity of the heating and is rather feeble, or else that the diurnal fluctuations of wind up to 100 km are generated by tropospheric heating. In contrast, the semidiurnal tide has a large scale depth which implies that the semidiurnal fluctuations of wind up to 100 km are associated with ozone heating. Areas of agreement and conflict with observation are mentioned, and several problems concerning data analysis and further theoretical work are outlined.

駿河灣東北隅淡島大謀網附近の海況に就きて

The present w ?? iter's seria' observations done several times a day at a station, 28m. deep and located near the keddle net (i.e., a sort of the guiding barrier) of Awasima Isle at the north-eastern end of Suruga Bay, spread over three periods, viz., April 27 to June 13, July 21 to August 1, and September 23 to October 10, 1931. The results may be summarised as follows:- 1) Specific gravity, transparency, and density of plankton fall but SiO2 content rises in the surface layer when the tida lcurrent brings water-mass from the mouth of the Kano River to this station. 2) In the bottom layer, temperature of water decreases but specific gravity and SiO2 content increase owing to upwelling of water-mass from below in consequence of tidal movement. 3) The flowing of water from the mouth of the Kano River to the upper layer at this station and the upwelling of the water-mass from below here take place alternately. 4) Such conditions of the sea as closely related to the tidal movement change with the same period as that of the tide, the maxima or minima appearing fortnightly besides diurnal and semi-diurnal fluctuations. 5) A heavy rain or a strong wind results to make considerable changes at the station by bringing an enormous amount of extremely turbid water from the Kano River to this place. Fragmentary as they are, the writer's observations made on June 7, 1931, in northern part of the bay appear to be worthy of record and may be briefly given in the following lines. 1) SiO2 content and specific gravity in the surface layer stand in close relation with each other, as is the case with the two variables in the corresponding layer at the station near Awasima Isle. 2) The surface layer of north-western part of the bay contains a very large amount of P2O5, its maximum value being found at the mouth of the Huzi River. 3) The 50m.- layer of northern part of the bay is remarkably rich in P2O5 content with its mean value about 120mg/m3, whereas the corresponding layers of the Tôkyô and Sagami Bays contain 30-50mg/m3 of the same. 4) The conditions of plankton sharply separate the northern coast of the bay from the coast of Nisiura which is situated just west to Awasima Isle. The plankton organisms along the former are mostly composed of zoöplankton and peridinians but are not densely populated. However, the diatoms lead the list along the latter and their density is very high.

Note by Mr. T. Hopkins on his paper on the semi-diurnal fluctuations of the barometer

"Note by Mr. T. Hopkins on his paper on the semi-diurnal fluctuations of the barometer." The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science, 28(188), p. 416

XXXI. On the causes of the semi-diurnal fluctuations of the barometer

(1846). XXXI. On the causes of the semi-diurnal fluctuations of the barometer. The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science: Vol. 28, No. 186, pp. 166-175.